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81SC Poor/ No start after storage help.

Hi all, looking for some of your collective wisdom with my starting problem.

I finished a full rebuild in the US on my 81SC in March this year. Engine started and ran perfectly under all conditions. Put around 800miles on the engine before shipping the car back with me to the UK.

Went to collect car in July. With a set of jump leads and 10ltrs of fresh fuel got a really poor low rpm chug-chug-chug running on 1cylinder, huge backfires through exhaust.

Engine never reached idle and would die pretty much straight away. Stored car until last week.

I have checked:

Plugs, fresh.
Another 10ltrs fuel.
With FP relay bridged pump runs.
With an 090 WUR, 26.4 to 10.4ohm cold to hot.
System pressure 4.6bar.
Control pressure 1.5 to 3.2bar.
Good residual pressure, tester valve open and closed.
Resistance at air plate, smooth movement, screeching and sound of injectors moving fuel.
I have tried priming cylinders by lifting airplane before starting. No difference.
I have tried a cold start at a range of control pressures. No difference.
Timing light showed sporadic activation but also very retarded timing.
Fresh but not new leads and cap.
Permatune CDI. Bosch blue coil.

Sorry for lengthy pre-amble!

So fuel pressure look good. Plus the starting or lack off shows no sensitivity to fuel input richer or leaner. Throttle also no effect.

Can the coil or CDI fail in an intermittent way like this? There is clearly some spark happening but perhaps at the wrong timing?

Last edited by Sub8; 01-20-2017 at 02:17 AM.. Reason: Edit to correct timing comment, retarded not advanced....
Old 12-13-2016, 10:43 AM
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Quote:
Originally Posted by Sub8 View Post
Timing light showed sporadic activation but also very advanced timing.
The US SC fires at near five degrees after top dead center when all is "factory". Maybe TDC or a smidgeon of advance, as I don't know how effective vacuum retard is when simply cranking for start.

Are you able to post a pic of the fastener stud/nut at the base of your distributor to provide a ball park reference of where your distributor is sitting right now with respect to adjustment?
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Old 12-13-2016, 03:24 PM
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Gummed up injectors due to no usage.

Bosch blue coil will 'work' but isn't right for CDI. Permatune, hmm.
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Old 12-13-2016, 03:52 PM
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Troubleshooting cold start problem........

James,

Sorry for not getting back to you ASAP. Just arrived in Tel Aviv when I got your email the other day and a very hectic schedule as tourist. If I were doing the test, I would do these tests:
a). Measure your cold control fuel pressures versus time. A 30-sec. intervals for 4 mins. (5 mins. max.). With the just FP running and take note of the ambient temp. The control fuel pressure profile could sometimes tell you right away if fuel is the culprit (?).
b). Connect an inductive light and observe for good and strong ignition signals during cranking or starting.
c). I saw your engine ran before you left for U.K. and it started right away. Six (6) months old fuel should be OK unless moisture developed during transport. Add some fuel stabilizer just in case. I strongly suggest to verify the integrity of your vacuum system and at this point refrain from tinkering the mixture setting.
d). Find a local friend that has an SC that you could test your CDI and coil. I could easily do this test for you if you were still living here in PA. Without a good and reliable ignition system, troubleshooting would be more challenging.

Keep us posted.

Tony
Old 12-13-2016, 04:21 PM
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The US SC fires at near five degrees after top dead center when all is "factory". Maybe TDC or a smidgeon of advance, as I don't know how effective vacuum retard is when simply cranking for start. Are you able to post a pic of the fastener stud/nut at the base of your distributor to provide a ball park reference of where your distributor is sitting right now with respect to adjustment?

Alternator nut at mid-point of slot, set to 5deg BTDC with timing light post engine rebuild on hot steady running engine.

Gummed up injectors due to no usage.

Injectors cleaned and flow checked prior to rebuild. Very unlikely to be gummed after 3-4months. Plus can hear fuel flow and have wet plugs on inspection.

a). Measure your cold control fuel pressures versus time. A 30-sec. intervals for 4 mins. (5 mins. max.). With the just FP running and take note of the ambient temp. The control fuel pressure profile could sometimes tell you right away if fuel is the culprit (?).

At approx 10C, 1.5bar control rising to 3.2bar after approx 3mins heating.

b). Connect an inductive light and observe for good and strong ignition signals during cranking or starting.

Done - slightly erratic light illumination (could be real issue, could be a function of the engine running so poorly?) 4 of the 6 plug leads checked in this fashion. Based on timing light ignition firing around 25 ATDC (very advanced).

c). I saw your engine ran before you left for U.K. and it started right away. Six (6) months old fuel should be OK unless moisture developed during transport. Add some fuel stabilizer just in case. I strongly suggest to verify the integrity of your vacuum system and at this point refrain from tinkering the mixture setting.

Agreed. Vac system was also refreshed at build. I have re-checked pipes etc, air plate does lift on its own during cranking / poor running.

d). Find a local friend that has an SC that you could test your CDI and coil. I could easily do this test for you if you were still living here in PA. Without a good and reliable ignition system, troubleshooting would be more challenging.

Again agreed - wish I was still in Philly (for a number of reasons!!!!!!). Not found anyone with this vintage of 911 yet!

Thanks all so far....
Old 12-14-2016, 02:00 AM
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Quote:
Done - slightly erratic light illumination (could be real issue, could be a function of the engine running so poorly?) 4 of the 6 plug leads checked in this fashion. Based on timing light ignition firing around 25 ATDC (very advanced).

Is the above a typo? If not, that's probably your problem.
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Old 12-14-2016, 08:23 AM
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CIS is all about fuel pressure. Put some gauges on it also dump a bottle of Techron in the gas tank.
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Old 12-14-2016, 08:47 AM
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Quote:
Originally Posted by Sub8 View Post
CDI fail in an intermittent way like this? There is clearly some spark happening but perhaps at the wrong timing?
Yes, a CDI can become intermittent, especially the potted Permatunes.
First, check all your grounds and then locate another CDI for testing.
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Old 12-14-2016, 01:07 PM
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Quote:
Originally Posted by mysocal911 View Post
Yes, a CDI can become intermittent, especially the potted Permatunes.
First, check all your grounds and then locate another CDI for testing.
Thanks for confirmation.

I've found a shop that will test my CDi and coil on one of their cars. Hopefully early next week.....
Old 12-16-2016, 03:05 AM
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Any update? Hope it was as simple as CDI, but interested if you fixed it some other way.


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Old 01-14-2017, 06:34 PM
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Hi - well some progress but still not 100% clear. Fuel system is OK.

I had the shop test my Permatune, apparently it was bad. I have replaced with a new Permatune and coil. When fitted made no difference to the issue.

I have now also fitted a new green disi pulse wire. I scoped the old and new pulse wire output while running the disi on the bench. Also stripped and cleaned / inspected the disi. I also removed the tacho output from the CDI box, just to remove another noise source.

Got it back together, set to TDC no1 as per procedure and got huge spark retard on cranking, like 70deg retarded (almost under the tinware clockwise on pulley). Removed disi turned rotor, refitted. Got spark near to 5deg BTDC.

She fired up! Still not a nice clean run-up as it was before but running.

However immediately after starting checking the timing shows it has moved from 5deg BTDC to around 35deg of advance, 10 o'clock on main pulley. WTF?

So now its hot the `idle` speed is way high around 3000rpm and with the disi body rotated to max allowed by slot I can only get the advance down to 15 or so deg.

Turn-off and leave it for 5mins. On restarting its reluctant again and its showing really retarded timing (again!!!, around 25deg or so), however it coughed into life and low and behold its now idling around 950ish RPM with 5Deg BTDC timing - WTF*2??????

Got it hot and while running removing the oil filler cap did not give a drop in RPM so now I am wondering if the backfiring and misfiring has popped a hose of or damaged the blow-off valve so next thing is to pressurize the intake and check for leaks.

Can anyone suggest a reason for the timing apparently moving by 80odd degs without actually moving the disi????????????
Old 01-20-2017, 12:53 AM
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Check the relay under the passenger seat next to the CIS module. It doesn't explain the odd timing changes but I'm guessing it could be the cause of the intermittent idle levels. You can jump two of the terminals but I can't remember which ones.
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Old 01-20-2017, 12:11 PM
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Troubleshooting......

James,

I would focus on two things:
a). Ignition distributor's operation and its integral components.
b). CDI

The unexpected change in the ignition timing from time to time is very alarming. This is something that would need serious effort to indentify and fix.

Tony
Old 01-20-2017, 12:43 PM
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Quote:
Originally Posted by boyt911sc View Post
James,

I would focus on two things:
a). Ignition distributor's operation and its integral components.
b). CDI

The unexpected change in the ignition timing from time to time is very alarming. This is something that would need serious effort to indentify and fix.

Tony
Hi Tony,

Disi has high axial play, somewhere around 1mm but wear pattern on drive gear looked ok.

Bob weights springs etc all in good condition and free. I could turn the top of the shaft relative to the bottom section with a little effort, it moved smoothly.

Pulse coil 577ohms

Core and star wheel all in good condition.

Pulse shape checked at CDI connector.

New CDI and coil. Ground checked as per installation instruction.

I must admit I'm starting to struggle a little with this problem!
Old 01-20-2017, 01:11 PM
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Quote:
Originally Posted by bgyglfr View Post
Check the relay under the passenger seat next to the CIS module. It doesn't explain the odd timing changes but I'm guessing it could be the cause of the intermittent idle levels. You can jump two of the terminals but I can't remember which ones.
Do not discount this advice. Make sure the clock is working. If not, that is the Lambda relay circuit. Move upstream from the relay for the culprit.

No need to check. Replace with new. This is an every day relay and if all else is ok, you will notice a slight improvement in how your car runs.

I pulled one out of a MB rear wiper motor and it worked under the seat in the SC.
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Old 01-20-2017, 01:49 PM
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Quote:
Originally Posted by Bob Kontak View Post
Do not discount this advice. Make sure the clock is working. If not, that is the Lambda relay circuit. Move upstream from the relay for the culprit.

No need to check. Replace with new. This is an every day relay and if all else is ok, you will notice a slight improvement in how your car runs.

I pulled one out of a MB rear wiper motor and it worked under the seat in the SC.
lambda circuit working correctly.

Any thoughts on why/how timing is moving?

When i was warming it up it ran well.

Can a faulty CDI affect timing assuming it's getting the correct pulse signal from Disi?
Old 01-21-2017, 10:04 AM
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Quote:
Originally Posted by Sub8 View Post
lambda circuit working correctly.

Any thoughts on why/how timing is moving?

When i was warming it up it ran well.

Can a faulty CDI affect timing assuming it's getting the correct pulse signal from Disi?
I doubt the CDI is the issue. The new P-Tunes do not have the issues like the old ones.

I cannot come up with a reason it could swing big retard to big advance.

Random thoughts. Timing light? Reluctor to stator gap consistent? Six pin connector allowing wires to talk to each other?
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Old 01-21-2017, 02:18 PM
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Quote:
Originally Posted by Sub8 View Post
Can anyone suggest a reason for the timing apparently moving by 80odd degs without actually moving the disi????????????
In my experience you can't get an accurate timing measurement with a strobe when cranking.

if you read your post disregarding all measurements you made while cranking, it makes perfect sense.
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Old 01-22-2017, 01:11 AM
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Quote:
Originally Posted by Sub8 View Post
I have now also fitted a new green disi pulse wire. I scoped the old and new pulse wire output while running the disi on the bench. Also stripped and cleaned / inspected the disi.

However immediately after starting checking the timing shows it has moved from 5deg BTDC to around 35deg of advance, 10 o'clock on main pulley?
You may have not connected the green wire correctly, as the polarity of the distributor
pulses are critical to proper timing over the full RPM range.
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Old 01-22-2017, 07:26 AM
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Originally Posted by mysocal911 View Post
You may have not connected the green wire correctly, as the polarity of the distributor
pulses are critical to proper timing over the full RPM range.
Hi. Yes I'm aware of that early 930? wiring difference on pulse wire.

I scoped original wire and checked replacement. So pulse s-wave rising from left hand side with sharp falling edge (firing edge) on the right hand side.

JonnyH care to elaborate on your last comment?

Checked pop off valve, possibly very slight leak at epoxy but strong vacuum holding valve closed. I've resealed it as a precaution.

Last edited by Sub8; 01-22-2017 at 11:01 AM..
Old 01-22-2017, 10:57 AM
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